Intrusion detection and location system

ABSTRACT

An intrusion detection and location system for perimeter protection comprises an elongated composite sensor line having a plurality of closely spaced coaxial electret cable transducers with known different sensitivities over their lengths and circuits responsive to electrical signals from the cables caused by mechanical vibrations applied to the cable by an intruder for producing an indication of the attempted intrusion and its location. Each of the cables has several longitudinal sections and laterally adjacent sections of the several cables have equal lengths and are respectively differently sensitized so that an intrusion occuring at one section generates in all the cables a binary coded output which uniquely identifies that section. In a preferred embodiment of the invention, the cable sections are either in a sensitized or non-sensitized state and the cables in successive sections are conditioned to produce a Gray code to minimize location errors for intrusions occuring at or near the junction of two sections. The cables are connected to processing circuits which decode the signals and transmit alarm and intrusion location information to the remote monitoring station.

ilnited States Patent [19] Armstrong Aug. 20, 1974 [75] Inventor: JohnE. Armstrong, Cupertino,

Calif.

[73] Assignee: GTE Sylvania Incorporated,

Mountain View, Calif.

[22] Filed: Sept. 4, 1973 [21] Appl. No.: 393,796

[52] US. Cl 340/261, 340/16 R, 340/258 D [51] Int. Cl. G081) 13/16 [58]Field of Search 340/16 R, 258 D, 261

[56] References Cited UNITED STATES PATENTS 2,345,771 4/1944 Reynolds340/261 2,435,996 2/1948 Baird 340/261 X 2,573,748 11/1951 Weinstein etal. 340/16 R 2,787,784 4/1957 Meryman et a1... 340/258 D 3,109,16510/1963 Bagno 340/258 D 3,132,330 5/1964 Donner 340/261 X 3,747,0577/1973 Brougher 340/16 R 3,750,127 7/1973 Ayers et al 340/261 3,763,48210/1973 Burney et al 340/258 R Primary Examiner-David L. TraftonAttorney, Agent, or Firm-John F. Lawler; Norman J. OMalley; Elmer J.Nealon SECTION SECTION SECTION SECTION SECTION SECTION SECTION A B C D lE F 6 57] ABSTRACT An intrusion detection and location system forperimeter protection comprises an elongated composite sensor line havinga plurality of closely spaced coaxial electret cable transducers withknown different sensitivities over their lengths and circuits responsiveto electrical signals from the cables caused by mechanical vibrationsapplied to the cable by an intruder for producing an indication of theattempted intrusion and its location. Each of the cables has severallongitudinal sections and laterally adjacent sections of the severalcables have equal lengths and are respectively differently sensitized sothat an intrusion occuring at one section generates in all the cables abinary coded output which uniquely identifies that section. In apreferred embodiment of the invention, the cable sections are either ina sensitized or non-sensitized state and the cables in successivesections are conditioned to produce a Gray code to minimize locationerrors for intrusions occuring at or near the junction of two sections.The cables are connected to processing circuits which decode the signalsand transmit alarm and intrusion location information to the remotemonitoring station.

7 Claims, 5 Drawing Figures y I ,le 19 1 IB CABLE H l o 1 o o 1 l ALARMCABLE I2 1 PROCESSOR AND o l l o INDICATOR 15min mmzolsm mPZEEEUmE j I lI I l l l l l r J l l I l r 1 muQOUmQ 2 2 2230 N 2 mm mfi 525 3 km vmBACKGROUND OF THE INVENTION This invention relates to intrusiondetection systems useful in perimeter detection.

A perimeter-type intrusion detection system described in US. Pat. No.3,763,482 utilizes a coaxial electret cable as a sensor line. The cableis tightly clamped to a chain link fence at intervals throughout itslength and constitutes a continuous transducer for converting fencevibration that may be caused by intruders into electrical signals whichare processed by appropriate discrimination circuits for activatingremote alarm apparatus. While this system has proven to be extremelyeffective in detecting intrusions, there remains the problem ofdetermining where the'intrusion has occurred With installations havingfence perimeters that are several hundreds of meters or more in length,knowledge of even the approximate location of the intrusion is oftenvital to effective follow-up action in protecting the property that isthreatened. This invention provides such location information.

A general object of this invention is the provision of an improvedperimeter protection system which automatically indicates the locationof the attempted intrusion along with an indication of the intrusionitself.

A further object is to provide such a system that is low in cost and isrelatively inexpensive to install.

SUMMARY OF THE INVENTION DESCRIPTION OF THE DRAWINGS FIG. 1 is a sideelevation of a portion of a chain link fence to which coaxial electretcables embodying the invention have been connected;

FIG. 2 is an enlarged cut-away portion of one of the coaxial cables ofFIG. 1 clamping rings; I

FIG. 3 is a transverse section taken on line FIG. 2;

FIG. 4 is a schematic view of the system embodyingthe invention showingadjacent sections of sensitized and unsensitized cable for producingbinary coded sig-' nals indicating the location of each of the severalsections; and

FIG. 5 is a detailed schematic block circuit diagram of the signalprocessing and alarm/indicator circuits.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, FIG.1 illustrates a chain link fence F supported by posts P in the ground Gand bordering-an area to be protected. The fence comprises a pluralityof longitudinal sections, two of the sections being indicated as C andD. If such a fence is equipped with a coaxial cable transducer system ofshowing the fence mounted the type described in US. Pat. No. 3,763,482,an alarm is givenwhen an intruder attempts to climb the fence at any ofthe several sections of fence. While this protection may be sufficientfor the particular requirement as when the risk of immediate damage tothe protected area or items in it by intruders is not great, there aremany applications when such risk is great so that additionally it isvital to know the location of the attempted intrusion. An example forsuch a need for intruder location information is a several acre storagearea for portable property items that are subject to hit and run thefttactics. Another example is the oil and gas storage tank area for arefinery that may be the target for sabotage or vandals. In each case,information on the approximate location of the intrusion is necessary inorder that prompt action may be taken for protection or recovery of theproperty.

In accordance with this invention, such intruder location information isobtained with the system comprising a composite sensor line 10consisting of three coaxial cables 11, 12 and 13 which are mounted onfence F over the length of the protected area. It is understood that thefence mounted embodiment is given by way of example and not by way oflimitation since the invention may be practiced also by burying thecables in the ground, disposing them under a floor or otherwise placingthem across the protected area. Furthermore, the cables might bepackaged in one sheath or sleeve to facilitate handling andinstallation. Cables ll, 12 and 13 are spaced closely together and aresecured to the main body of the fence by clamp rings 14 so as to providea tight mechanical coupling between the fence and cables. One of theadjacent ends of the cables is open while the opposite ends areconnected to a signal processor circuit l6 illustrated in FIG. 1 asbeing buried in the ground G. Electrical output signals generated by thetransducing action of the three cables in response to vibrations on thefence are processed by circuits 16 which eliminate false alarm signalsand determine by a logic function tobe described the location along thefence of the disturbance producing the signals. The output of circuit 16is transmitted by line 18 to alarm and indicator apparatus 19 at aremote monitoring station; the alarm signifies that an intrusion istaking place and the indicator identifiesthe location of that intrusion.1

The details of construction of cables 11 and 12 are explained in US.Pat. No. 3,763,482. Briefly, each cable, cable 11 for example, comprisesan inner conductor 21, see FIGS. 2 and 3, an outer conductor 22, adielectric filler 23 between these conductors and an outer syntheticinsulating cover 24 on outer conductor 22. Dielectric filler 23 is anelectret and produces an electrical signal between conductors 21 and 22when a mechanical force causes relative motion between the dielectricand the outer conductor of the cable. Each of the clamp rings 14 tightlysecures the cable to the main body of the fence, shown in FIGS. 2 and 3as strands 26, so that vibrations induced in the fence by an intruder orthe like climbing it cause a signal to be generated across conductors,21 and 22.

The sensitivity of such a coaxial cable transducer is determined by theamount of charge on the electret filler 23. One technique for making theelectret as explained in the aforementioned patent is to apply a d-cpotential of predetermined magnitude across the conductors 22 and 23while the heat softened filler 23 cools and solidifies. The amount ofcharge on the filler generally varies proportionally with the magnitudeof the applied d-c biasing voltage. The sensitivity of this electretcable'as that term is used herein means the signal strength or voltageproduced across the outer and inner conductors at one end of the cableper unit of impact force applied exteriorly to the cable.

The sensitivities of cables 11, 12 and 13 at various points throughouttheir lengths differ so that the sensitivity combination of the threecables at one such point is different from similar sensitivitycombinations at all other such points. By varying the sensitivitycombination of the three cables in this manner, the severallongitudinally distributed points on the composite sensor line areprovided with predetermined sensitivity codes which uniquely identifythose points or locations, respectively. In a preferred form of theinvention, the sensitivity of each cable varies between two levels, ahigh level of approximately 1 microvolt per micrometer of indention anda low level preferably at zero. It will be understood, however, thatmore than two sensitivity levels may be used to obtain a location codewith slightly more sophisticated processing circuitry.

In the embodiment of the invention shown in FIG. 1, each of cables l1,l2 and 13 is composed of a longitudinal series of cable sectionsdetachably or otherwise connected together by connectors 28 located, forexample, at fence posts P. Two such sections are designated as C and Din the drawing. The juxtaposed row of cables comprising each sectionhave the same lengths and the pattern or combination of cablesensitivities varies from section to section in the predetermined mannerdescribed above. Thus the location of an intrusion with this cablearrangement can be made to the accuracy of one cable section.

When cables having two levels of sensitivity are used, the number ofsensitivity-coded sections into which a protected boundary may bedivided is determined by the number of cable transducers that are usedin accordance with the expression Where S is the number of sections andN is the number of cable transducers. Thus a two-cable system permitsdivision of the protected line into three sections (S 2 -1 =4-l =3), athree-cable system yields seven sections, a four-cable system l5sections and so on. If more than two sensitivity levels are used,the'foregoing expression becomes where L is the number of sensitivitylevels. For example, a three-cable (N 3) system with three sensitivitylevels (L 3) could produce 26 sensor line sections. The accuracy of thelocation data is therefore dependent upon the number of sensor cablesand sensitivity levels that are used and this is dictated by the desiredsystem resolution and cost. It should be noted that coaxial cabletransducers of the type described above are relatively inexpensive perunit length and the increase in installation costs of four cables, forexample, as compared to three cables is insignificant.

FIG. 4 illustrates seven sections A G, inclusive, of cables 11, 12 and13 with sensitivities varying between a zero level indicated in heavyline and designated by the binary digit 0 and a predetermined positivelevel indicated by the unshaded line and designated by the binarydigit 1. Each of the seven sections of the cables has a sensitivity codewhich is different from the other sections so that the output signalsfrom the three cables is a binary coded word which uniquely designatesthe particular section from which the signal was generated as by anattempted intrusion or other disturbance. By way of example, the binaryword 001 generated by the three cables 11, 12 and 13 in that orderdesignates Section A whereas the word 100 denotes Section G. This outputof the cables is decoded in processor 16 and, if caused by an intruder,energizes alarm and indicator unit 19.

An important feature of the invention is that the section codingarrangement is a Gray code. That isto say, the sensitivity patternbetween any two adjacent sections is such that only one cable changessensitivity. If an intruder should attempt to climb the fence at or nearthe junction of two sections so as to excite a sensitized conductor inboth sections, the maximum location error generated is one section. Forexample, assume an intruder attempts to cross Section B near itsjunction with Section C. Since according to the Gray code only cable 11changes its sensitization state, the code of 1 10 or Section C would betransmitted, thus limiting the error to within one section.

Processor 16 comprises a signal sensor 30, see FIG. 5, a discriminator31 and a binary decoder 32. Sensor 30 comprises bistable flip-flops 34,35 and 36 having inputs connected to cables l1, l2 and 13 and outputsconnected to lines 37, 38 and 39, respectively. Each flip-flop of thesensor is also connected by line 40 to a manual reset mechanism 41. Eachof flip-flops 34, 35 and 36 produces a logic 0 on its output line untila signal is received from corresponding sensor cable and produces alogic l from the first instant such signal is received until theflip-flop is manually reset to produce a O by an input on reset line 40.These flip-flops change state when an analog input from the respectivesensor line rises above a preset value.

Discriminator 31 is designed to recognize characteristics of the analogsignal produced by the coaxial cable sensors when produced by anintruder. By way of example, discriminator 31 is capable of recognizingand passing signals defining the signature of a man climbing or cuttingthe fence or digging under it. At the same time, this circuit rejectsspurious signals such as those produced by wind, birds landing on thefence, cattle rubbing against the fence, etc. In its simplest form,sensor 31 comprises bandpass filters 42 and 43 connected to the outputsof cables 11, 12 and 13 in parallel with signal sensor 30 and havingbandpass characteristics covering those parts of the frequency spectrumwithin which the signals of interest lie. The outputs of bandpassfilters 42 and 43 on lines 44 and 45, respectively, are connectedrespectively to flip-flops 48 and 49, each of which produces a logic 0output until a signal is received from the corresponding bandpassfilter. As with the signal sensor circuit 30 described above, theseflip-flops change to the l state upon receipt of a signal from thebandpass filter and remain in that state until reset by manual reset 41to which they are connected by lines 40 and 50. The outputs offlip-flops 48 and 49 on lines 52 and 53, respectively, are combined inan OR gate 54 which produces on line 55 a single output, i.e., a logicO," if no intruder is present and a logic l if an intruder is present.

While two channels only have been shown in discriminator 31, morechannels may be included for providing a more selective discriminationas required or desired. Similarly, additional discrimination may beprovided with integration and threshold circuits as desired or required.

Binary decoder 32 comprises AND gates 56, 57 and 58 having inputsconnected to signal sensor output lines 37, 38 and 39, respectively, andto the output 55 of OR gate 54 via line 59. The outputs of these ANDgates on lines 61, 62 and 63, respectively, are connected to abinary-to-decimal decoder 65 having a plurality of output lines 66,seven as shown corresponding to the seven cable sections, respectively,shown in FIG. 4. By way of example, decoder 65 may readily be derivedfrom a Signetics N7442 decoder manufactured and sold by SigneticsCorporation, Sunnyvale, Calif.

Remote unit 19 comprises an alarm unit 68 connected to the output line55 of discriminator OR gate 54 by line 69 and an indicator 70 having aplurality of lamps 71, seven for this embodiment, connected respectivelyto the outputs 66 of decoder 65. Alarm unit 68, which may be a bell,flashing light or the like is energized whenever an intrusion occurs andone of the lamps 71 of indicator 70 is energized to designate the one ofthe seven sections of the sensor cables at which the intrusion hasoccurred.

In operation, an intrusion occurring, for example, in Section D of thecables, see FIG. 4, generates a l digital word on cables ll, 12 and 13,respectively. The outputs from the cables to sensor 30 cause flip-flops34 and 35 to change from the 0 state to the I state while the remainingflip-flop 36 is unchanged because the unsensitized portion of cable 13generates no signal. This produces a digital word signal of 1 10 onsignal sensor output lines 37, 38 and 39 as one input to AND gates 56,57 and 58, respectively, of binary decoder 32. Simultaneously,discriminator 31 receives and processes the outputs from the cables andpasses them if they meet the bandpass and other criteria for signals ofinterest, i.e., those generated by an intruder. The output from OR gate54 of the discriminator energizes alarm 68 and provides the other of thetwo inputs to AND gates 56, 57 and 58 of the binary decoder. Thus thebinary decoder is operative only if the signals on the sensor cablesmeet the established criteria for an intruder. The binary coded word 110on AND gate output lines 61, 62 and 63, respectively, is logicallyinterpreted by decoder circuit 65 to energize the indicator lamp 71which designates Section D of the sensor cables.

What is claimed is:

1. A disturbance detection system comprising a plurality of elongatedcontinuous transducers disposed along a boundary being monitored andadapted to produce output electrical signals in response to themechanical force applied to the transducers,

said transducers being juxtaposed whereby a disturbance occurring at anylocation along said boundary applies a substantially equal force to allof the transducers,

where S is the number of sections, N is the number of transducers and Lis the number of sensitivity states,

the sensitivity codes for the sections being different whereby thecomposite signal output of said transducers contains informationindicating both a disturbance along said boundary and its location,means for coupling to said transducers mechanical forces produced by thedisturbance to be detected,

means for processing the composite output signals from said transducersfor producing an output signal designating the section of transducers atwhich the disturbance occurred, and

means responsive to said output signal from said processing means forgiving an alarm and indicating the location of said disturbance. 2. Thesystem according to claim 1 in which the pattern of variation of saidsensitivity states of said sections of transducers is in accordance withthe Gray code.

3. The system according to claim 1 in which L 2, said processing meanscomprising signal sensor means responsive to the outputs from saidtransducers for translating same into binary coded form and binarydecoder means for converting said binary coded signals into saidsection-designating output signal.

4. The system according to claim 3 in which said processing means alsoincludes discriminator means responsive to the outputs of saidtransducers for passing signals of interest and rejecting other signals,producing an output only if the transducer outputs contain signals ofinterest, said binary decoder means being connected to saiddiscriminator means and being enabled by said output of the latter.

5. A perimeter-type intrusion detection system comprising a plurality ofjuxtaposed coaxial electret cables adapted to produce output electricalsignals in response to mechanical vibrations produced by an intruder,

each of said cables comprising a plurality of sections in longitudinalseries, laterally adjacent sections of said cables being coextensive andaligned in rows,

the transducing sensitivity states of the cable sections beingcharacterized by a high level and a low level whereby excitation of arow of sections by an intruder produces a coded composite output signalfrom the plurality of cables corresponding to the sensitivity states ofthe sections in the row,

each row having a different section sensitivity pattern relative to theother rows whereby the code of said 7 s composite output signal isindicative of the excited 6. The system according to claim in which thenumrow, ber of said cables is at least three.

means for decoding Said Coded composite Sign and 7. The system accordingto claim 5 in which the value means responsive to said decoded signalfor indicat- 5 of Said low Sensitivity level is Zeroing the excitedsection.

1. A disturbance detection system comprising a plurality of elongatedcontinuous transducers disposed along a boundary being monitored andadapted to produce output electrical signals in response to themechanical force applied to the transducers, said transducers beingjuxtaposed whereby a disturbance occurring at any location along saidboundary applies a substantially equal force to all of the transducers,each of said transducers comprising a plurality of sections inlongitudinal series, laterally adjacent sections of said transducersbeing coextensive and having equal lengths and comprising rows, thetransducing sensitivity of the sections being in at least two differentstates whereby the combination of electrical output signals from thetransducers caused by a disturbance represents a code, the maximumnumber of sections of said transducers being given by the expression SLN - 1 where S is the number of sections, N is the number of transducersand L is the number of sensitivity states, the sensitivity codes for thesections being different whereby the composite signal output of saidtransducers contains information indicating both a disturbance alongsaid boundary and its location, means for coupling to said transducersmechanical forces produced by the disturbance to be detected, means forprocessing the comPosite output signals from said transducers forproducing an output signal designating the section of transducers atwhich the disturbance occurred, and means responsive to said outputsignal from said processing means for giving an alarm and indicating thelocation of said disturbance.
 2. The system according to claim 1 inwhich the pattern of variation of said sensitivity states of saidsections of transducers is in accordance with the Gray code.
 3. Thesystem according to claim 1 in which L 2, said processing meanscomprising signal sensor means responsive to the outputs from saidtransducers for translating same into binary coded form and binarydecoder means for converting said binary coded signals into saidsection-designating output signal.
 4. The system according to claim 3 inwhich said processing means also includes discriminator means responsiveto the outputs of said transducers for passing signals of interest andrejecting other signals, producing an output only if the transduceroutputs contain signals of interest, said binary decoder means beingconnected to said discriminator means and being enabled by said outputof the latter.
 5. A perimeter-type intrusion detection system comprisinga plurality of juxtaposed coaxial electret cables adapted to produceoutput electrical signals in response to mechanical vibrations producedby an intruder, each of said cables comprising a plurality of sectionsin longitudinal series, laterally adjacent sections of said cables beingcoextensive and aligned in rows, the transducing sensitivity states ofthe cable sections being characterized by a high level and a low levelwhereby excitation of a row of sections by an intruder produces a codedcomposite output signal from the plurality of cables corresponding tothe sensitivity states of the sections in the row, each row having adifferent section sensitivity pattern relative to the other rows wherebythe code of said composite output signal is indicative of the excitedrow, means for decoding said coded composite signal, and meansresponsive to said decoded signal for indicating the excited section. 6.The system according to claim 5 in which the number of said cables is atleast three.
 7. The system according to claim 5 in which the value ofsaid low sensitivity level is zero.